The present invention is directed to thermoformable composites of flame-retardant polycarbonate and woven glass cloth suitable for use in aircraft interiors.
The Federal Aviation Administration (FAA) upgraded its fire and smoke standards for aircraft interior components on Aug. 20, 1990. The FAA dropped the allowable heat-release rate for materials governed under Federal Aviation Regulation (FAR) 25.853, which includes ceiling and wall panels, partitions, outer surfaces of galleys, large cabinets, and storage compartments. The heat-release test used, ASTM E906, subjects a sample of a material to 3.5 watts/cm.sup.2 of radiant heat and the heat subsequently released from the sample is determined. The earlier standards required a maximum of 100 kW/min/m.sup.2 of heat release during the first two minutes and a peak release of 100 kW/m.sup.2 during a five-minute period (100/100 rule). The recent requirements dropped the allowable heat-release rate to 65/65.
Restrictions on smoke release for aircraft interior component materials have also been implemented. A maximum specific optical smoke density of less than 100 is required by most aircraft manufacturers (based on four-minute samples), as determined under ASTM E662. The material must also meet the flammability requirements of FAR 25.853(a) and (a-1) which requires the component material be self-extinguishing when tested vertically (60 seconds exposure to a Bunsen burner flame) in accordance with FAR 25, Appendix F (Part IV). Furthermore, the materials must meet burn-through requirements under FAR 25.853 according to FAR 25, Appendix F, Part III and toxicity requirements by aircraft manufacturers.
Heretofore, aircraft interior components have comprised reinforced composites utilizing phenolic resins as the matrix material. Phenolic resins have been used because of their high heat resistance, rigidity, adhesion to reinforcements, and solvent resistance. While phenolic resins appear to satisfy the new FAA requirements, the aircraft industry is still seeking a more flame-resistant thermoplastic composite material. Materials which exceed the FAA requirements are sought in contemplation of further restrictions by the FAA. For these and other reasons, the individual airlines have their own smoke- and gas-release limits, flame spread index, and burn-through requirements.
Cost pressures have directed efforts toward the development of plastic materials with improved flammability characteristics since their use reduces manufacturing costs and weight penalties associated with fabricated metal parts.
For a new airplane interior component to be readily accepted in the market, its architecture and function must be compatible with existing airplane structures for retrofitting purposes. In addition to meeting flammability requirements, these interior components should at least maintain, if not improve, the durability and maintainability of previous parts with a weight no greater, and preferably less, than that of existing parts. The same is true for functions such as the ease of installation and removal. Additionally, the components should be capable of accepting a variety of decorative effects and configurations as determined by each individual airline.
ULTEM.RTM. polyetherimide has been found to provide the required flammability performance in non-reinforced films. This material is vacuum thermoformable, allowing low-cost processing. However, without reinforcement, these ULTEM.RTM. polyetherimide films require thick sections to meet the stiffness requirements of certain interior components, such as a sidewall panel. In addition, it can be difficult, if not impossible, to meet burn-through requirements without reinforcement.
Aircraft interior components comprised of 40-50 wt % ULTEM.RTM. polyetherimide/knitted woven glass cloth composites require less material and provide excellent flammability performance and improved stiffness. It is desirable to provide a less costly component with similar performance however. It is also desirable to provide such a composite which can be prepared from conventional continuous process equipment which operates at temperatures below about 250.degree. C.